Clade Trilobite from the Paleozoic Era. Trilobites have a flattened oval body, a segmented exoskeleton divided into three parts, compound eyes and podomere limbs with branching gills (biramous).
Trilobites were one of the most successful class of animal in the history of the planet existing for over 300 million years - spanning almost the entire Paleozoic Era. Though predominantly found in the shallower margins, trilobites were abundant throughout the oceans of the world and their fossil remains have been found on every continent.
There have been over 20,000 different species of trilobite discovered, ranging across 10 orders. They exhibit numerous anatomical adaptations that helped them survive in almost every niche of the marine environment. Because of their wide variety and distribution over such an extensive period of time, trilobites have become one of the most important index fossil for earth scientists and evolutionary biologists. This is not only because of their ability to mark points in time but also that they serve as examples of how the mechanics of evolution work in conjunction with changing environmental conditions.
Trilobites had remarkable compound eyes made up of thousands of hexagonal calcite cells. These cells acted as individual lenses and were very durable with some even able to polarize light. It is presumed that many trilobites had excellent vision. There are indications that a few trilobite species even developed forward depth of vision. As this is seen as a requirement for effective predation it has added to the speculation that some trilobites evolved into agile hunters that swam in search of prey.
Fossil remains have been a source of fascination for many thousands of years and trilobites have been found in ancient burial sites, presumably being used as talismans. In more recent times they have become major collector items.